There is presently employed a type of three wall construction in low to mid-rise buildings (about ten floors or less) in which brick or masonary veneer wall is backed up with over steel stud mounted dry wall covered with a moisture barrier. An interior dry wall layer forms the third wall. The brick or veneer is typically held to the building by ties extending from interior vertical stringers or is screwed into such stringers. The dry wall back-up is provided as a water, vapor and wind barrier protecting the interior of the building from these environmental conditions. A significant problem associated with this construction is the water permeability of the brick or masonary veneer and corrosion of the brick/veneer attachment hardware. This problem is discussed in an article entitled "Brick Veneer: A Second Opinion", C. T. Grimm, THE CONSTRUCTION SPECIFIER. April, 1984.
In addition to the corrosion problems associated with the masonary mounting hardware, I believe there will be a significant corrosion problems associated with the interior steel framing used to mount the dry wall and to hold the brick or masonary veneer as well as damaging moisture penetration due to eventual deterioration of the dry wall back-ups currently being specified and installed. A typical dry wall mounted back-up is provided today by mounting U-shaped galvanized steel channels to the facing upper and lower slab surfaces with power driven steel fasteners, mounting galvanized steel studs at regular intervals (typically 16 inches on center) between the floor and ceiling channel members with sheet metal steel screws and hanging half-inch gypsum board panels to the studs by means of screws or other wallboard fasteners, again typically of steel. The installed gypsum board panels are then typically "dampproofed" by a roofing or dampproofing mechanic who attaches a treated felt paper or trowels a dampproofing mastic over the exterior surface of the panels. Mastic is perceived to be a more effective moisture barrier though more expensive treatment than felt paper which can be torn or pierced in mounting and can separate from adjoining layers. Masons then follow to install the brick or masonary veneer, often puncturing the felt paper or mastic and underlying dry wall with wall ties. An interior dry wall is also hung to the interior sides of the studs supporting the dry wall back-up. Although galvanized steel is generally used, the galvanized surface protection is often abraded when the mounting elements are connected to one another leaving unprotected steel at the critical junction points.
A significant problem with this type of dry wall back-up construction is the high labor cost, particularly that associated with applying the "dampproofing". The installers often must be paid a craftsman wage and the "dampproofing" material must be applied to the entire surface of the installed back-up dry wall by hand.
Yet another problem associated with mastic-type dampproofing systems as currently installed is that no provision is made for eventual deterioration of the mastic between abutting dry wall panels. Typically, the material is applied by hand as quickly as possible with no special treatment being given to the seams between adjoining gypsum board panels. The mastic is simply troweled across the panels and seams between panels. The thickness of the hand applied coating is never uniform. Typically only a minimum thickness is specified for the wall covering both the gypsum board surfaces and the seams. Asphalt based mastics, which are most commonly specified, can embrittle with curing. The seams between adjoining dry wall panels are also subject to movement due to dynamic flexture of the building under wind loads and, I believe, will eventually cause cracking of the typically thin mastic layer overlapping the seams creating a source for moisture entry. Depending upon the mastic used, temperature fluctuations may also create stresses tending to cause embrittled mastic to eventually crack in the seam areas.